The present invention relates to an autoleveling device of a headlamp for an automobile which serves to automatically adjust tilting (hereinafter referred to as autoleveling) for an optical axis of the headlamp in a direction of off set equivalent to tilting in a longitudinal direction of a vehicle (hereinafter referred to as a pitch angle) based on the pitch angle, and more particularly to an autoleveling device for automatically adjusting the optical axis of the headlamp vertically based on the pitch angle of the vehicle mainly during stop.
In a headlamp of this kind, for example, a reflector having a light source inserted therein is supported to be tilted around a horizontal tilting axis with respect to a lamp body and an optical axis of the reflector (headlamp) can be tilted around the horizontal tilting axis by an actuator.
In a conventional autoleveling device, a vehicle is provided with pitch angle detecting means, a vehicle speed sensor, a control section for controlling the driving operation of the actuator based on a detection signal therefrom and the like, and an optical axis of a headlamp (reflector) is adjusted to be always set in a constant state with respect to a road.
In the conventional autoleveling device, however, leveling is carried out in real time for a change in a vehicle posture which is caused by acceleration and deceleration during running and a change in a load which is caused by loading and unloading a luggage or causing an occupant to get in and off during the stop irrespective of the running and stop of the vehicle. For this reason, the number of operations of the actuation is very large and power consumption is great. Furthermore, a great deal of durability is required for driving mechanism components such as a motor or a gear. Thus, a cost is increased.
In order to provide an inexpensive autoleveling device which has the driving frequency of an actuator reduced and can be used for a long period of time, therefore, there has been proposed an autoleveling device (Japanese Patent Application No. Hei 10-274859) in which the driving operation of an actuator is controlled at a constant interval (10 seconds) during stop.
In the autoleveling device thus proposed, the driving operations of the actuators of a pair of left and right headlamps are controlled at the same time based on pitch angle data which are previously detected corresponding to an interval time. If an amount of a change in the pitch angle data for a stop position (a position of an optical axis) of the actuator is small, there is a possibility that the actuator of one of the headlamps might be driven and the actuator of the other headlamp might not be driven (autoleveling might function in one of the headlamps and might not function in the other headlamp).
This problem is investigated. As a result, it has been found that the problem arises due to a hysteresis of an actuator driving circuit.
More specifically, a driving circuit using a DC motor M shown in FIG. 6 is used as an actuator mechanism for tilting a reflector. A motor driver serves to control driving (rotation) of the DC motor M which is an actuator body in response to a driving signal sent from a control unit, and a signal is fed back from a potentiometer which detects a rotating position of the motor M to the motor driver. In the motor driving circuit, a pair of switches Sw1 and Sw4 (or switches Sw2 and Sw3) are turned on to rotate the motor M and a pair of switches Sw1 and Sw3 on the Hi side (or switches Sw2 and Sw4) are turned on to brake and stop the motor when the potentiometer reaches a target position as shown in FIG. 7. Also after the motor is braked, it continuously rotates by inertia. Therefore, a hysteresis having predetermined widths of H1 and H2 shown in FIG. 8 is provided between the braking and operation of the motor such that the motor does not carry out a hunching operation.
FIG. 8 shows a hysteresis in an actuator (motor) driving circuit. A feedback signal sent from the potentiometer indicates a current position of the actuator (motor). Therefore, a difference between an actuator driving signal and the feedback signal sent from the potentiometer indicates an operation position of the actuator. When the difference between the actuator driving signal and the feedback signal sent from the potentiometer (which will be hereinafter referred to as an actuator driving signal output) reaches almost 0 (a position indicated as the reference numeral P2 or P3 in FIG. 8), the actuator driving circuit is braked and stopped. When the actuator driving signal output is increased to be equal to or less than P1 or equal to or more than P4 in FIG. 6, the actuator (motor) is operated. Thus, the hysteresis is provided in the actuator driving circuit.
However, the actuator such as a motor is an industrial product. Therefore, a hysteresis range always has an error. The hysteresis widths of the respective actuator driving circuits of the left and right headlamps are not identical to each other. For this reason, if pitch angle data detected by pitch angle detecting means and pitch angle data used for the last driving control of the motor has a small difference when the motor is to be operated in the stop state, an actuator driving signal output corresponding to the pitch angle data gets out of the hysteresis range in the actuator driving circuit of one of the headlamps and gets in the hysteresis range in the actuator driving circuit of the other headlamp. In such a case, one of the actuators is driven and the other actuator is not driven. As a result, the autoleveling functions in one of the headlamps and does not function in the other headlamp. Consequently, the positions of the optical axes of the left and right headlamps make a difference.
The invention has been made in consideration of the problems of the conventional art and has an object to provide an autoleveling device of a headlamp for an automobile which can drive left and right actuators at the same time without influence of a hysteresis of an actuator driving circuit.
In order to achieve the object, a first aspect of the invention is directed to an autoleveling device of a headlamp for an automobile comprising a pair of left and right headlamps in which optical axes are tilted in a vertical direction with respect to a body by driving operations of respective actuators, single control means for controlling the driving operations of the actuators at the same time, vehicle speed detecting means for detecting a speed of a vehicle, pitch angle detecting means for detecting a pitch angle of the vehicle, and a storage section for storing pitch angle data of the vehicle which are detected by the pitch angle detecting means, the control means controlling the driving operation of the actuator such that the optical axes of the headlamps are set in a constant tilting state with respect to a road based on the pitch angle data detected by the pitch angle detecting means, wherein the control means drives the actuator if a difference between the pitch angle data detected by the pitch angle detecting means and the pitch angle data used for the last driving control of the actuator is more than a predetermined reference value which is equal to or more than a pitch angle equivalent to a hysteresis width of each of actuator driving circuits of the left and right headlamps, and does not drive the actuator if the difference is less than the reference value.
If the difference between the pitch angle data detected at the present time by the pitch angle detecting means and the pitch angle data used for the last actuator driving control is greater than the predetermined reference value which is equal to or greater than the pitch angle equivalent to the hysteresis width of each of the actuator driving circuits of the left and right headlamps, both actuators are driven. Contrary, if the difference is less than the predetermined reference value, the actuators are not driven. Therefore, there is no drawback that only one of the actuators is driven as in the conventional art.
The function of the control means will be described with reference to FIGS. 4A and 4B showing the hysteresis of each actuator driving circuit of the left and right headlamps.
In the actuator driving circuit of the left headlamp, hysteresises HL1 and HL2 are present as shown in FIG. 4A. In the actuator driving circuit of the right headlamp, hysteresises HR1 and HR2 are present as shown in FIG. 4B. A predetermined reference pitch angle xcex80 which is equal to or more than a pitch angle equivalent to hysteresises HL and HR of the left and right actuator driving circuits is preset, to the control means, as a reference value to be a reference for driving the actuator. Ho in FIGS. 4A and 4B represents a hysteresis width corresponding to a reference pitch angle xcex80, and H0/2 greater than HL1(HL2) and H0/2 greater than HR1(HR2) are obtained.
The control means decides whether a difference |xcex82xe2x88x92xcex81| between pitch angle data xcex82 newly detected by the pitch detecting means and pitch angle data xcex81 used for the last control of the actuator is more than the predetermined reference pitch angle xcex80. Only if the difference |xcex82xe2x88x92xcex81| is more than the predetermined reference pitch angle xcex80 (|xcex82xe2x88x92xcex81| greater than xcex80), both actuators are driven at the same time. Accordingly, there is no possibility that one of the actuators might be driven.
A second aspect of the invention is directed to the autoleveling device of a headlamp for an automobile according to the first aspect of the invention, wherein the control means controls the driving operation of the actuator at regular intervals based on the detected pitch angle data during stop and controls the driving operation of the actuator only once based on pitch angle data for stable running only during the stable running in which a vehicle speed having a predetermined value or more and an acceleration having a predetermined value or less are continuously maintained for a predetermined time.
Since the pitch angle data obtained during the stop of the vehicle have few disturbance factors for the detection, they are more accurate than the pitch angle data obtained during the running of the vehicle. The driving operation of the actuator is controlled based on the accurate pitch angle data. Therefore, the autoleveling can be carried out accurately.
Moreover, the driving operation of the actuator is controlled during the stop every constant time (interval time). Consequently, an operation frequency of the actuator is decreased, power consumption is reduced and driving mechanism components are less worn.
Furthermore, in the case in which the leveling (optical axis correction) based on the pitch angle data during the stable running in which a vehicle speed having a predetermined value or more and an acceleration having a predetermined value or less are continuously maintained for a predetermined time (data close to the pitch angle data obtained during the stop of the vehicle) properly corrects leveling (optical axis correction) based on the pitch angle data during the improper stop of the vehicle as in the case in which the vehicle is stopped on a slope or the vehicle is stopped while running onto a curb.
A third aspect of the invention is directed to the autoleveling device of a headlamp for an automobile according to the second aspect of the invention, wherein a driving interval of the actuator is longer than a maximum driving time of the actuator which is required for one leveling.
If the interval between the last control and the next control is shorter than the maximum driving time of the actuator, the actuator starts a next operation before reaching a target value. Consequently, the driving frequency of the actuator is increased so that the lifetime of the actuator might be reduced. After the actuator reliably reaches the target value through the last control, the actuator is driven through the next control. Therefore, the driving frequency of the actuator is decreased correspondingly so that the lifetime of the actuator can be prevented from being reduced.
By increasing the interval of the driving operation of the actuator, a change in the pitch angle in the interval from the last control to the next control can be omitted without the driving operation of the actuator. Therefore, all the operations between the intervals are aggregated into the driving operation of the actuator in the next control. Correspondingly, the driving frequency of the actuator is decreased.
Moreover, the pitch angle data of the vehicle which are detected by the pitch angle detecting means are always fetched into the control section and are calculated as a control volume also for a driving interval period of the actuator. By utilizing all the pitch angle data fetched into the control section as control data, more pitch angles can be used as the control data and it is possible to carry out proper leveling with the detection of an accurate posture (pitch angle) of the vehicle.
A fourth aspect of the invention is directed to the autoleveling device of a headlamp for an automobile according to the second or third aspect of the invention, wherein the control means controls the driving operation of the actuator based on vehicle pitch angle data detected before an accelerator is stepped on which are not influenced by a change in a posture of a vehicle during starting when the interval control is carried out almost simultaneously with the start of the vehicle.
The start of the vehicle is detected by the vehicle speed detecting means (vehicle speed sensor). In the case in which the interval control is carried out simultaneously with the start of the vehicle, the driving operation of the actuator might be controlled based on the improper pitch angle data. Therefore, the autoleveling can be carried out properly by correcting and controlling the driving operation of the actuator based on the proper pitch angle data obtained before the accelerator is stepped on.
This respect will be described in detail with reference to FIG. 3. FIG. 3 is a chart showing a change in a vehicle speed and a vehicle posture until the vehicle starts to run and carries out constant-velocity running after the accelerator is stepped on.
As shown in FIG. 3, a predetermined time (T) is required while the accelerator is stepped and the vehicle then starts to run actually. In other words, the vehicle speed starts to be increased after the predetermined time (T) passes since the accelerator has been stepped on. For this reason, there is a predetermined start detection delay time T after the accelerator is stepped on until the vehicle speed sensor detects the start of the vehicle.
On the other hand, the acceleration rapidly acts on the vehicle posture when the accelerator is stepped on. Consequently, a rear portion of the vehicle once sinks. While the acceleration acts, this state (in which the rear portion of the vehicle sinks) is continuously maintained. More specifically, when the vehicle speed sensor detects the start of the vehicle (the control section detects the start of the vehicle based on the output of the vehicle speed sensor), the rear portion of the vehicle is maintained to sink (forward and upward).
Consequently, in the case in which the driving control of the actuator (for example, the interval control) is carried out almost simultaneously with the start of the vehicle (in the case in which there is a timing of the interval control within the vehicle start detection delay time T required after the accelerator is stepped on until the vehicle speed sensor detects the start of the vehicle), the pitch angle data used for the interval control are detected by the pitch angle detecting means in the timing of the interval control and might include data on the state in which the vehicle sinks when the running is started, which is not always appropriate. More specifically, there is a possibility that the driving operation (autoleveling) of the actuator based on improper pitch angle data might be carried out.
By using the pitch angle data during the stop which are detected before the time T (pitch angle data detected before the accelerator is stepped on which is indicated as the reference designation A in FIG. 3), the driving operation of the actuator is corrected and controlled. Consequently, it is possible to avoid the influence of a change in a vehicle posture during the start of the vehicle in the autoleveling of the headlamp.
Before the vehicle actually takes off after the accelerator is stepped on, 1 to 3 seconds are taken depending on the vehicle. For this reason, it is desirable that the vehicle start detection delay time should be set to 1 to 3 seconds. Moreover, in the case in which the start of the vehicle is detected within a preset time (set to 1 to 3 seconds) after the interval control (the driving control of the actuator), it can be decided that the interval control (the driving control of the actuator) is carried out almost simultaneously with the start of the vehicle. By setting the preset time within the vehicle start detection delay time (1 to 3 seconds), it is possible to easily decide whether or not the interval control is carried out almost simultaneously with the start of the vehicle (whether or not the timing of the interval control is coincident when the vehicle takes off).
A fifth aspect of the invention is directed to the autoleveling device of a headlamp for an automobile according to any of the first to fourth aspects of the invention, wherein the driving operation of the actuator is controlled on lighting conditions.
As long as the headlamp is not turned on, the actuator is not driven. Correspondingly, the number of the operations of the actuator can be decreased, power consumption can be reduced and driving mechanism components are less worn.